C SPECIFICATION

       void GLAPIENTRY glTexGend( GLenum coord,
                                  GLenum pname,
                                  GLdouble param )
       void GLAPIENTRY glTexGenf( GLenum coord,
                                  GLenum pname,
                                  GLfloat param )
       void GLAPIENTRY glTexGeni( GLenum coord,
                                  GLenum pname,
                                  GLint param )

PARAMETERS

       coord   Specifies a texture coordinate.  Must be  one  of  GL_S,  GL_T,
               GL_R, or GL_Q.

       pname   Specifies  the  symbolic name of the texture-coordinate genera-
               tion function.  Must be GL_TEXTURE_GEN_MODE.

       param   Specifies a single-valued texture generation parameter, one  of
               GL_OBJECT_LINEAR, GL_EYE_LINEAR, or GL_SPHERE_MAP.

C SPECIFICATION

       void GLAPIENTRY glTexGendv( GLenum coord,
                                   GLenum pname,
                                   const GLdouble *params )
       void GLAPIENTRY glTexGenfv( GLenum coord,
                                   GLenum pname,
                                   const GLfloat *params )
       void GLAPIENTRY glTexGeniv( GLenum coord,
                                   GLenum pname,
                                   const GLint *params )

PARAMETERS

       coord  Specifies  a  texture  coordinate.   Must  be one of GL_S, GL_T,
              GL_R, or GL_Q.

       pname  Specifies the symbolic name of the texture-coordinate generation
              function  or  function parameters.  Must be GL_TEXTURE_GEN_MODE,
              GL_OBJECT_PLANE, or GL_EYE_PLANE.

       params Specifies a pointer to an array of  texture  generation  parame-
              ters.  If pname is GL_TEXTURE_GEN_MODE, then the array must con-
              tain  a  single  symbolic  constant,  one  of  GL_OBJECT_LINEAR,
              GL_EYE_LINEAR,  or  GL_SPHERE_MAP.   Otherwise, params holds the
              coefficients  for  the  texture-coordinate  generation  function
              specified by pname.

DESCRIPTION

       is  used,  where  g  is  the value computed for the coordinate named in
       coord, p1, p2, p3, and p4 are the four values supplied in  params,  and
       xo,  yo,  zo,  and  wo  are the object coordinates of the vertex.  This
       function can be used, for example, to  texture-map  terrain  using  sea
       level  as a reference plane (defined by p1, p2, p3, and p4).  The alti-
       tude of a terrain vertex is computed by the GL_OBJECT_LINEAR coordinate
       generation  function  as its distance from sea level; that altitude can
       then be used to index the texture image to map white  snow  onto  peaks
       and green grass onto foothills.

       If the texture generation function is GL_EYE_LINEAR, the function

                                g=p1xe+p2ye+p3ze+p4we

       is used, where

                              (p1p2p3p4)=(p1p2p3p4)M-1

       and  xe,  ye, ze, and we are the eye coordinates of the vertex, p1, p2,
       p3, and p4 are the values supplied in params, and M  is  the  modelview
       matrix  when glTexGen is invoked.  If M is poorly conditioned or singu-
       lar, texture coordinates generated by the  resulting  function  may  be
       inaccurate or undefined.

       Note  that the values in params define a reference plane in eye coordi-
       nates.  The modelview matrix that is applied to them  may  not  be  the
       same  one  in  effect  when the polygon vertices are transformed.  This
       function establishes a field of texture coordinates  that  can  produce
       dynamic contour lines on moving objects.

       If  pname  is  GL_SPHERE_MAP  and coord is either GL_S or GL_T, s and t
       texture coordinates are generated as follows.  Let u be the unit vector
       pointing  from  the  origin to the polygon vertex (in eye coordinates).
       Let n sup prime be the current  normal,  after  transformation  to  eye
       coordinates.  Let

                                     f=(fxfyfz)T
       be the reflection vector such that

                                     f=u-2n?n?Tu

       Finally,  let m=2?f<I>x+f<I>y+(fz+1)2.  Then the values assigned to the s and
       t texture coordinates are

                                       s=f_x<I>m_+_

                                       t=f_y<I>m_+_

       To enable or disable a  texture-coordinate  generation  function,  call
       glEnable or glDisable with one of the symbolic texture-coordinate names
       (GL_TEXTURE_GEN_S,     GL_TEXTURE_GEN_T,      GL_TEXTURE_GEN_R,      or
       GL_TEXTURE_GEN_Q) as the argument.  When enabled, the specified texture
       defined  value,  or when pname is GL_TEXTURE_GEN_MODE and params is not
       an accepted defined value.

       GL_INVALID_ENUM is generated when pname is GL_TEXTURE_GEN_MODE,  params
       is GL_SPHERE_MAP, and coord is either GL_R or GL_Q.

       GL_INVALID_OPERATION  is  generated if glTexGen is executed between the
       execution of glBegin and the corresponding execution of glEnd.

       glGetTexGen
       glIsEnabled with argument GL_TEXTURE_GEN_S
       glIsEnabled with argument GL_TEXTURE_GEN_T
       glIsEnabled with argument GL_TEXTURE_GEN_R
       glIsEnabled with argument GL_TEXTURE_GEN_Q

       glActiveTextureARB,           glCopyPixels,           glCopyTexImage2D,
       glCopyTexSubImage1D,      glCopyTexSubImage2D,     glCopyTexSubImage3D,
       glTexEnv,  glTexImage1D,  glTexImage2D,  glTexImage3D,  glTexParameter,
       glTexSubImage1D, glTexSubImage2D, glTexSubImage3D



                                                                  GLTEXGEN(3G)